Conventional gearboxes for vehicles employ synchronizer rings to ensure smooth shifts between gears in the gearbox. The synchronizer rings ensure that the shift collar and the desired gear make frictional contact before the teeth of the collar engage the gear. In this way, the rotational speeds of the gearshafts in the gearbox are progressively synchronized, thereby allowing a gearshift to take place without any mis-engagement of the collar teeth and the desired gear.
Synchronizer rings add significantly to the cost of manufacture of a gearbox. As a result, there have been a number of proposals put forward in order to remove the need for synchronizer rings in gearboxes. In removing the synchronizer rings, there is a need to ensure synchronization of the rotational speeds of the gearshafts in another way before a gearshift can be allowed to occur. Otherwise, the mis-engagement, referred to above, can still occur, leading to difficulties in achieving a shift, and also potentially damaging the gearbox components. Therefore, when removing the synchronizer rings from a gearbox, it is important to ensure that a shift cannot take place until the synchronization of the gearshaft speeds has occurred.
Synchronizerless shifting mechanisms have been previously proposed. UK Patent Application GB 2 335 010 (GB '010) discloses a synchronizing unit which synchronizes the rotational speeds of a layshaft and output shaft in a gearbox. The unit comprises first and second auxiliary gears which are fitted to respective first ends of the layshaft and output shaft. The unit further comprises a solenoid-controlled clutch on the output shaft for accelerating the layshaft, and a solenoid-controlled brake for slowing down the layshaft. The brake is applied to one of the first or second auxiliary gears to slow the layshaft. A controller monitors shaft speeds and gear selector positions in order to control the unit.
Unfortunately, the unit disclosed in GB '010 is fitted as a “bolt-on” onto the end of the gearbox, so that the auxiliary gears can be fitted onto the ends of the respective shafts. As a result, adding the unit to a gearbox may increase the overall size of the gearbox. In the vast majority of vehicles, it is an objective that gearboxes are of certain dimensions so that they fit within the spaces designed for them. The unit of GB '010 can therefore compromise design requirements in existing vehicles, and in many instances may prove difficult to retro-fit to conventional gearboxes due to the increased size.
Additionally, the unit of GB '010 may result in added weight and in complexity of introducing a brake to slow down the layshaft. In using a brake, a number of further mechanical components are added to the gearbox. Not only do these components increase the overall weight of the gearbox, but they may also be subjected to very large friction forces. By increasing the complexity of the gearbox and subjecting the added components to such forces, the risk of malfunction or breakdown also may be increased.
The present disclosure is directed to one or more improvements in the existing technology.